Structural reinforcements are commonly employed within motor vehicle doors to provide some level of protection against intrusion into the passenger compartment by objects impinging against the vehicle door. A common form of door reinforcement is a metal stamping which is welded to the interior of the door.
Welding the reinforcement to the door commonly induces significant distortion of the door. The metal stamping may vary from its nominal shape due to the "spring back" phenomenon associated with stamping operations. Distorted reinforcements are forced to their nominal shape for welding to the door. When the door and the reinforcement assembly are subsequently released, the reinforcement reacts against the door, causing it to twist. Additional door distortion may be introduced by the heating effect of the high temperatures associated with welding on the stamping. Doors so distorted are one source of alignment problems between the door assembly and a surrounding body structure door frame.
It is known to provide a structural reinforcement which is free to rotate relative to the door at both ends. One such reinforcement has an elongated tubular bar mounted to the door by trapping enlarged ends of the bar in conical sleeves at the ends or edges of the door. Because the ends are free to rotate, the reinforcement introduces effectively no torsional distortion of the door. Upon loading, the bar deflects, reacting against the sleeve. Increased loading results in increased distortion of the sleeves. This design, however, is sensitive to variations in both distance between the sleeves and the length of the reinforcement. Slight variations in either the length of the reinforcement, or the distance between the sleeves, significantly affects the resultant impact resistance of a door with this type of reinforcement. An axially loose assembly would result in additional bar deflection being sustained before sleeve deflection is initiated. This would likely result in a lower reinforcement strength and a significantly greater amount of intrusion into the passenger compartment for a given impact force than would an assembly with minimal variance between the reinforcement ends and the associated brackets.
It is desired to provide a structural reinforcement for a vehicle door inducing no distortion of the door upon installation and providing a resistance to intrusion relatively insensitive to the installation process.